Heat-sensitive compositions and elements, and processes for using same



llnited States atent 3,063,863 Patented Nov. 13, 1962 iee 3,063,863 EAT-SENSITIVE COMPOSITIONS AND ELE- MENTS, AND PROCESSES FOR USHWG SAME Russell Sedgwick Holland, Milltown, and Robert Ellis Wayrynen, Little Silver, NJL, assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Apr. 21, 1959, Ser. No. 807,761

6 Claims. (Cl. 11736.8)

This invention relates to heat-sensitive compositions and elements embodying them that are useful in thermographic recording and copying systems. More particularly, it relates to such compositions and elements which upon exposure to heat darken in color and undergo the further transformation whereby the water-soluble components become water-insoluble. Still more particularly, this invention relates to heat-sensitive flexible sheets bearing coatings containing such compositions. v. Heat-sensitive paper for use in a thermographic apparatus giving copies of certain graphic originals quickly and easily by a completely dry process is commercially available. The primary shortcomings of this paper (which has enjoyed considerable commercial use) are (1) its limited resolving power due to the granular structure of the heat-sensitive components, and (2) the narrow exposure latitude. Other disadvantages are the unattractive appearance of the finished copy caused by the uppleasant combinations of image and background color, the thermal instability of the paper after it is used for making copies and the undesirably high flexibility of the material.

An object of this invention is to provide a heat-sensitive element which is capable of forming rapidly, by a dry thermographic process, an image having high resolving power. A further object is to provide such a product which provides wide exposure latitude. A still further object is to provide an element capable of forming a dark-colored image on a white or light-colored background having improved appearance and good legibility. Additional objects are to provide an element which is thermally stable after the initial image has been formed and has good handling characteristics. Still other objects will be apparent from the following description of the invention.

The heat-sensitive compositions of this invention comprise an intimate mixture of (1) A S-hydroxy-3-pyrrolin-2-one, having a negative substituent in the 3-position, of the general formula:

HO/ \N/ Bi l wherein X is a negative substituent selected from the group consisting of quaternary onium and inium salts and carboxyl groups and groups hydrolyzable thereto, R is a member selected from the group consisting of hydrogen, monovalent hydrocarbon radicals of not more than carbon atoms, amino and dialkyl amino of l-2 carbons, the radicals R when separate can be the same or different and are each selected from the group consisting of hydrogen, alkyl of 1 through 10 carbon atoms, cycloalkyl of 4 through 6 carbon atoms, aryl of 6 through 10 carbon atoms and alkaryl of 7 through 10 carbon atoms and the R's when together constitute a single divalent hydrocarbon radical that forms with the 4- and S-carbon atoms of the pyrrolincne ring a carbocyclic radical of 5 to 7 ring atoms, said substituted pyrrolinones being further characterized in that only one of the 4- and S-carbon atoms have an aromatic substituent;

(2) A small amount of a metal salt taken from the group consisting of cupric, ferrous, mercuric and silver salts of a monoor dibasic organic carboxylic acid, and if desired,

(3) A polymeric binding agent, and

(4) A solvent or diluent.

In the preferred aspect of the invention, the metal salt is a cupric salt of an organic carboxylic acid of not more than4 carbon atoms which is either unsubstituted or may be substituted by halogen, e.g., fluorine, chlorine and bromine, hydroxyl, amino or alkylamino of 1-4 carbon atoms. These compositions can be made by merely admixing the compounds and, if desired, a solvent or diluent and a polymeric binding agent, e.g., a natural or synthetic water-permeable colloid having protective colloid properties, e.g., gelatin and polyvinyl alcohol.

The novel heat-sensitive copy of recording elements of the invention comprise a suitable support having an outer surface coated or impregnated with the aforesaid compositions. The supports can be rigid, e.g., glass, plastic plates, or cardboard, or they can be flexible, e.g., paper or a polymeric film. Flexible supports are preferred. The support for the thermally sensitive, permanent imagerecording elements of the invention can vary widely in constitution but should not be a good conductor of heat because the image is produced thermally and a heat-conductive support, e.g., a metal foil or a self-supporting film or layer containing an appreciable quantity of powdered metal, would precent the formation of a sharp image. In general, the flexible support can be composed of an organic polymeric material having a softening point above the temperature at which the thermographic image is formed, e.g., above l20200 C. Suitable such polymen'c materials include paper, thin cardboard, self-supporting films composed of cellulose and regenerated cellulose; cellulose others, eg., methyl cellulose, ethyl cellulose of low substitution; cellulose esters, e.g., cellulose triacetate; synthetic macro-molecular polymers, including polyvinyl acetals, e.g., polyvinyl formal; polyvinyl esters, e.g., polyvinyl acetate of low acetate content, and proteins, e.g., gelatin. Instead of films, the foregoing synthetic polymers can be layers on paper or another support. The supports can be used in the form of films and in the form of felted sheets made from fibers of the cellulosic or other polymeric materials referred to above.

The following symbolic diagrams illustrate two embodiments of the invention:

Coated and/ or impregnated heat-sensitive layer containing 5-hydroxy-3-pyrro1in-2-one and Cu, Fe, Hg or Ag salt of monoor dibasic organic carboxylic acid Support, e.g., paper or polymeric film Heat-sensitive layer of organic colloid binder, S-hydroxy- 3-pyrrolin-2-one and Cu, Fe, Hg or Ag salt of m0noor dibasic organic carboxylic acid Support, e.g., paper or polymeric film For some uses the flexible sheet support should be infrared-transparent to permit the formation of the color image in depth and in, for instance, reflex copying to permit the satisfactory development of the image on the reverse surface or within the sheet. For other uses, for instance, recording paper for a suitably driven hot stylus, the flexible sheet support can be infrared opaque. The flexible sheet support can be transparent or opaque to visible light. For contrast purposes, it is generally desirable that the flexible sheet support be somewhat opaque to visible light and, ideally, should exhibit a color which contrasts to the colorof th thermographic image.

The optimum ratio of the hydroxypyrrolinone and metal salt will dependupon the type of product desired but, in general, the preferred range is considered to be 0.1 to 0.5 mols of the metal salt per mol of the substituted hydroxypyrrolinone compound with a useful range extending from 0.01 to 1.0 mols of metal salt per mol of the substituted hydroxypyrrolinone. Increasing the relative concentration of metal salt increases the speed of the thermochemical reaction but this may be at the expense of higher background density or stain depending on the particular metal ion employed. This background is, of course, no problem when the print can be washed. Thermographic speed also is increased by increasing total coating weight of the heat-sensitive materials. Useful hydroxypyrrolinone coating weights are in the range 20-5 mg./dm. depending on intended application, while the preferred coating weight range is 50-200 mg./dm.

In exemplification of a preferred embodiment of this invention, an aqueous solution of 3-cyano-4,5dimethyl- 5-hydroxy-3-pyrrolin-2-one and cupric acetate are coated on paper or other suitable base material and exposed as described in C. S. Miller U.S. Patent 2,740,896 of April 3, 1956, in a commercial Thermo-Fax (made by Minnesota Mining and Manufacturing Co.) thermographic copying machine, whereby there is produced a copy of a graphic original, said copy having an intense dark-colored, grainless, high resolution image against a light-colored badground.

The invention will be further illustrated by but is not intended to be limited by the following examples.

EXAMPLE 1 3-cyano-4,5-dirnethyl-5-hydroxy-3-pyrrolin-2-one 104 mg.) and 34.2 mg. of Cu(CH COO) -H O were dissolved in 4 ml. of water at room temperature and, after standing for 1 hour, the solution was brush-coated onto a 4" x 4" piece of onionskin paper (Eagle-A Trojan). The coating, after being air-dried at room temperature, was exposed at the No. 1 setting of a Premier Model 19 Thermo-Fax (Minnesota Mining and Manufacturing Co.) thermographic copying machine to produce a copy of a paper sheet on which letter characters were printed in carbon black ink, said copy having a coal black image against a light colored background.

EXAMPLE II To 1 g. of a solution of 100 g. of polyvinyl alcohol (99% hydrolyzed, viscosity of 4% aqueous solution centipoises at 20 C.) in 900 g. of water were added 0.25 ml. of a 1 molar solution of 3-cyano-4,5-dimethyl-S- hydroxy-3-pyrrolin-2-one and 0.60 ml. of a 0.1 molar cupric acetate solution. The mixture was allowed to stand overnight at room temperature and was coated with the aid of a doctor knife on a 2 x 3 piece of tracing paper. The dried coating was exposed as in Example I to pro duce a copy having a coal black image against a lightcolored background.

EXAMPLE III in Example II were mixed, the resulting solution allowed to stand for 1 hour at room temperature, spread out over the surface of a 2" x 2" area of the treated film base. and then air dried at room temperature to yield a smooth, transparent coating. The coating was exposed as described in Example I to yield a copy having a coal black image against a light colored background.

EXAMPLE IV Six and six-tenths ml. of the hydroxypyrrolinone solution of Example Ii, 8.8 ml. of a 0.15 molar cupric acetate solution and 6.7 ml. of a solution of 15 g. of deionized gelatin dissolved in g. of water were mixed, allowed to stand for an hour at room temperature, and a portion of this reaction mixture was spread uniformly over the surface of a 4 x 4" piece of polyethylene terephthalate film base which had been made and coated with a vinylidene chloride/methyl acrylate/itaconic acid copolymer and gelatinsubstrata as disclosed in Alles U.S. Patent 2,779,684. After air drying at room temperature, the coating was exposed as described in Example I to yield a copy having a coal black image against a light'colored background.

EXAMPLE V 3-cyano-4,S-dirnethyl-S-hydroxy-3-pyrrolin-2-one (608 mg.) was dissolved in 4 ml. H O, to which was added 2.4 ml. of 0.3 molar Cu(CI-I CO0) solution. This mixture without prior aging was coated on an 8 /2 x 11" sheet of onionskin paper and the coating was air-dried. It was then exposed for 2 passes at the No. 1 setting of the copying machine for Example I to produce a copy of a paper sheet on which letter characters were printed in carbon black ink, said copy having a black image on a light bluegreen background.

A portion of this exposed coating was dipped for 30 seconds in water, blotted to remove excess water and air dried. The black letters remained unchanged by this treatment while the background became a very faint pinkishblue which is stable to atmospheric humidity. This paper upon heating for 1 minute at 180 C. turned very slightly yellowish, the image remaining essentially unchanged.

Another portion of the coating was dipped for 30 seconds in water, drained, and then dipped for 10 seconds in 0.1 M HCl solution, followed by a 30-second water wash. It was then air dried. The background was a pure white, while the image remained a coal black. Heating at 180 C. up to 1 minute had no efiect on the copy so treated.

EXAMELE VI A solution of 0.25 g. of 3-cyano-4,S-dimethyl-S-hydroxy-3-pyrrolin-2-one in 3 ml. of water was mixed with 0.15 ml. of 0.3 M Cu(CH COO) solution to give a Cu +/hydroxypyrrolinone mol ratio of 0.027. The miX- ture was coated fresh on a 5 x 8 /2 inch piece of onionskin paper and air dried. Its sensitivity was tested by heating a small disk of the coating on a Fisher melting point apparatus, the temperature of the metal block being read by a thermometer whose bulb was inserted inside the block. The coating darkened somewhat after holding 20 seconds at 150 C. and was a dark gray-black after 20 seconds at 180 C.

The above procedure was repeated several times in all details except for the use of increasing quantities of Cu(Ci-I COO) solution which resulted in increasing the ratio Cu++ /hydroxypyrrolinone. The effect on thermographic sensitivity is shown in tabular form below.

Table I w/ Volume 0.3 M ydroxypyr- 'Ilicrrnographic Effects CutGHaCOO): rolinone mol ratio 0. 027 Some darkening after 20 sec. at 150 0.

Dark grey-black after 20 sec. at 180 C. Darkening after 20 sec. at 135 C. Darkening after 20 sec. at 120 0.

Dark grey-black at 135 C. Pronourgced darkening after 20 see.

Slight darkening after 20 see. at 0. Jet block otter 20 sec. at C.

A mixture which contained 5 millimols of 3-cyano-4,5- dimethyl-5-hydroxy-3-pyrrolin-2-one in aqueous solution and 1 millimol of Cu(CH COO) in aqueous solution was brought up to a volume of 10 ml. by addition of water. Approximately one ml. of this mixture was evenly spread, with the aid of a small brush, over the surfaces of 3" x 4" pieces of each of the following papers:

(a) Onionskin paper (Eagle-A Trojan) paper.

-(b) Tracing paper (Keuffel and Esser No. 195L Albanene) from the surface of which the wax treating material had been removed with acetone.

() A high-grade bond paper.

(d) A very thin (55 g./sq. m.), 100% rag-based, translucent, non-coated photographic paper stock.

After drying in air at room temperature, the four coated papers were exposed as in Example I to yield copies having coal black images against light-colored backgrounds. The four coatings were roughly equivalent in thermographic sensitivity.

EXAMPLE V-IH One gram of a solution of polyvinyl alcohol as described in Example 11 was coated on a 2" x 3" piece of tracing paper (Albanene) and air-dried at room temperature. A mixture of 0.25 ml. of an aqueous l M solution of 3-cyano-4,S-dimethyl-S-hydroxy-3-pyrrolin-2- one and 0.60 ml. of an aqueous 0.1 M solution of mercuric acetate was allowed to stand overnight and then flowed over the surface of the polyvinyl alcohol treated tracing paper. After air drying at room temperature, the coating was exposed as in Example I to yield a copy having a dark purple image against :a light pink background.

EXAMPLE IX To 0.6 ml. of a 0.1 M Fe(CH COO) solution, there was mixed with 0.25 ml. of an aqueous 1 M solution of 3-cyano-4,5-dimethyl-5-hydroxy-3-pyrrolin-2-one and 1 g. of the polyvinyl alcohol solution described in Example II. After standing overnight, the mixture was coated on a 2" x 3" piece of tracing paper (Albanene). Exposure as in Example I yielded a copy having a brownishblack image against a yellowish tan background.

EXAMPLE X To 0.85 g. AgNO dissolved in 5 ml. pure, distilled water there were added 5 ml. of an aqueous 1 M NaOH solution. The resultant Ag O precipitate was separated from the supernatant liquid by centrifugation and to the precipitate was added slowly a acetic acid solution in which the brown Ag O precipitate dissolved. The silver acetate solution thus formed was diluted with water to a total volume of 50 ml. to give an 0.0725 M solution.

A mixture of 0.80 ml. of the 0.0725 M AgOCOCH solution and 0.25 ml. of an aqueous l M Solution of 3-cyano-4,5-dimethyl-5-hydroxy-3-pyrrolin-2-one was coated on a polyvinyl alcohol treated tracing paper support described in Example VIII. With drying and exposure as described in Example I, there was formed a copy having a dark brown image against a lighter brown background.

A similar coating upon appreciable exposure to room light showed indications of photolysis so that with such a coating it is desirable to provide for protection against excessive exposure to light prior to the thermographic exposure. The fixing step following thermographic exposure (as described in Example V) is particularly recommended for a coating containing silver.

EXAMPLE XI which was added an amount of the solution or suspension containing 0.1 millimol of the respective copper salt. These mixtures were coated on 3" x 4" pieces of onionskin paper and air dried at room temperature. Each of the respective coated papers showed some color changev when heated for 15-30 sec. at C. and turned black upon heating for the same length of time at 180 C.

EXAMPLE m1 '(a) Approximately 41.5 mg. (0.25 millimol) of 3-cyano-(4,5-methyl, ethyl)-5-hydroxy-3-pyrrolin-2-one was dissolved in 2 ml. ethanol. To this solution was added 0.15 ml. of 0.3 M Cu(CH COO) solution and the mixture coated fresh on a 2 X 3" piece of onionskin paper. After air-drying the coating was exposed to a printed paper sheet in the Thermo-Fax machine described in Example I. Three exposure passes at setting No. 1 produced a faint black image on a light blue-green background.

(b) The procedure described in the preceding paragraph (a) was repeated but using 48 mg. of 1-allyl-3- cyano-4,5-dimethyl-5-hydroxy-3-pyrrolin-2-one in 1 ml. ethanol instead of the pyrrolin-Z-one described therein. The reaction product of this hydroxypyrrolinone with copper acetate yielded a faint brown image on a light greenish-tan background.

(0) The procedure of paragraph (a) was repeated but using 48.5 mg. of 1-dimethylamino-3-cyano-4,5-dimethyl- 5-hydroxy-3-pyrrolin-2-one in 1 ml. ethanol instead of the pyrrolin-Z-one of that paragraph. The reaction product of this hydroxypyrrolinone with copper acetate yielded a faint brown image on a light green background.

(d) 93 mg. (0.5 millimol) of 3-thiocarbamyl-4,5-dimethyl-5-hydroxy-3-pyrrolin-2-one was dissolved in a small quantity of a water-methanol mixture. To this was added 0.3 ml. of 0.3 M Cu(CH COO) solution and the mixture coated fresh on a 3" x 4" piece of onionskin paper. After air-drying the coating was heated on a melting point block as described under Example VI, yielding a brown-black color after 15 sec. at C. The color before heating was a medium brown.

Addition of many copper salts of organic acids with exclusion of foreign ions requires preparation of the organic copper salt compound from Cu(OH) and the appropriate organic acid. The following procedures are useful for this purpose.

Procedure A.To make Cu(OH) 8.53 gm. (0.05 mole) CuCl -H O was dissolved in 50 ml. H O. To this was added with stirring 50 ml. of 1 M NaOH solution. A slight excess of NaOH was added to raise the pH to 8 to 9. After filtering, the Cu(OH precipitate was washed with water.

Procedure B.-To make copper propionate, one-half of the Cu(OH) precipitate from Procedure A was mixed with 1.80 ml. of propionic acid and the mixture diluted to 50 ml. with water to make a 0.5 M suspension. Additional propionic acid was required to dissolve all the Cu(QH) forming a clear green solution.

Procedure C.To make copper chloroacetate, one-half of the Cu(OH) precipitate from Procedure A was mixed with a solution of 2.30 grams chloroacetic acid in 25 ml. H O. The mixture, also a suspension, was diluted to 50 ml. with water. Additional chloroacetic acid was required to dissolve all the Cu(OH) Procedure D.To make copper glycinate, 0.02 mole of Cu(OH) was prepared as described in Procedure A to which was added a solution of 1.50 g. glycine dissolved in 25 ml. H O. The slurry was diluted to 100ml. with P1 0. A few drops of cone. HCl was added to help dissolve the suspension.

Procedure E.Copper glycolate and copper pyruvate were made in a manner similar to that described for copper giycinate, except that 2.17 grams of 70% glycolic acid solution and 1.76 grams of pyruvic acid Were used in place of the glycine. Also, excess glycolic and pyruvic acids, respectively, were used instead of concentrated a scess HCl to complete dissolution of the CuKOI-Dg. The copper pyruvate, however, was observed to decompose on standing. A solid material separated, but remained sus pended, while an unidentified gas was evolved.

Procedure F .-Copper trifiuoroacetate was prepared by mixing 0.02 mole of Cu(OH) with 1.49 ml. triiluoroacetic acid followed by dilution to 100' ml. with H O. No attempt was made to dissolve the small portion of Cu(OH) that did not dissolve.

Procedure G.Cupric salts of the following acids were made by dissolving the amounts of acid specified below in about 1 ml. H O, adding 118 mg. of commercial basic copper carbonate and heating very gently to drive off CO These mixtures did not dissolve completely and were evaluated as suspensions.

(a) 104 mg. malonic acid 7 Y (b) 136 mg. alpha,alpha'-oxydiacetic acid 360 mg. acetylsalicylic acid (d) .068 ml. formic acid Production of the thermographic image in the new elements of the present invention can be achieved in any way whereby the element comprising the flexible sheet support and in operative association therewith the hydroxypyrrolinone and metal salt is selectively exposed to the required color-developing temperatures to form the desired pattern. For instance, the thermographic element can be pressed with a heated stylus operated manually or mechanically as the recording or copy arm of a sensing system driven by a photoelectric scanning beam. In a similar fashion, heated type characters, slugs, or cornplete composed plates may be pressed directly in contact with the thermographic element. Alternatively, the therinog'raph'ic images can be prepared by suitable selective infrared absorption. Thus, a master to be reproduced will generally have a dark text on a white background. Accordingly, on exposure to infrared radiation or to normal light, the black areas are selectively warmer than the white areas by virtue of the selective absorption of the infrared radiation in the dark areas. With light of suflicient intensity directed on such an original held in contact with one of the thermographic elements of the present invention, the original is heated in the dark areas to temperature ranges wherein the thermographic reaction occurs in the therrnographic element, thereby producing a colored direct positive duplicate of the original.

The temperatures to which these thermographic elements must be brought in order to develop the thermographic image will vary with the specific substituted hydroxypyrroiinone, the nature of the support, the relative concentration of the hydroxypyrrolinone, the specific metal ion and the amount of such ion. Generally satisfactory colored images are obtained when the thermographic element is brought to temperatures between about 120 C. and about 200 C. A generally satisfactory average temperature would thus be in the neighborhood of about 140170 C. The times at which these thermographic elements must be selectively held at such temperatures in order to develop satisfactory image quality likewise vary with the nature of the substituents on the hydroxypyrrolinone, themetal salt and in part with the nature of the support in the sense of the optical contrast qualities thereof. An approximate shortest color development time at these temperatures is in the neighborhood of about 0.1-2.0 seconds; whereas, with some of the less reactive mixtures of lower heat sensitivity, reaction times of up to 1015 seconds or even a minute are needed. Generally speaking, an average color development time at the average development temperature of about 175 C. will be about 1.0 to 2.0 seconds.

The primary use for the thermally-sensitive elements is as a thermographic copying paper, for example as a general copying paper. The elements are also useful as a thermogr'aphic microfilm, for making copies via enlargement or reduction projection and for use in recording information in recording instruments, e.g., spectrograms. I

This invention has the advantage that it provides thermally-sensitive recording elements of high potential resolving power since it is a grainless system as contrasted with the non-grainless commercially available systems described in US. 2,663,654 through 2,663,657. Exposure latitude of the element is unusually broad. This invention makes possible the production of a copy which is pleasing to the eye, giving an intense black image against a white of light-colored background.

Further advantages are the excellent thermal stability which can be achieved in a copy which has been subjected to a simple fixing operation, the good handling characteristics derived from satisfactory performance of the element in existing exposure devices to produce the desired direct positve copy without having to go through a negative intermediate. 7

These advantages are in addition to those resulting from the simplicity of use of the elements in a completely dry processing image formation and the rapidity with which a finished copy may be produced.

Another advantage of the present invention is that it provides the art with a new class of thermally sensitive image recording elements which are economical to make and easy to use in making positive images directly. The novel elements do not require skilled operators or technicians when used to make positive images. A large number of reproductions can be made rapidly from any printed or other material'to be copied. Another advantage is that the novel elements can be readily fixed to remove discoloration and obtain a white background bywashing in wateror dilute mineral. acid (e.g., hydro"- chloric solutions). Still other advantages will be apparent to those skilled in the art of image formation or reproduction.

The novel thermally-sensitive recording elements of this invention have advantages over prior art elements when used in charts to be marked with a stylus. The latter generally employ a dark-colored paper with a white, opaque coating that becomes clear on application of heat, thereby producing a dark area on a white background. Typical coatings of this type are based on opaque, waxy, or crystalline materials, blushed resin coatings (see U.S. Patent 2,519,660) or plastic films coritaining microscopic voids (see US. Patent 2,739,909). Waxy coatings stick to adjacent layers and because of their softness are easily damaged. The blushed resin coatings must be applied under carefully controlled conditions to avoid variations in opacity of the coatings. The third type of film-that containing the microscopic Voidsis widely used, but careful balancing of ingredients is required to produce a film which can be marked at available temperatures but at the same time is not unduly sensitive to pressure. All of these prior types ofcoatings must be applied to a colored base, which is generally paper carrying a dark pigmented coating. In addition, volatile organic solvents are necessarily employed in the production of all three types.

What is claimed is:

'1. A thermo-sensitive, image-recording copy element comprising a support of low heat conductivity having an outerrstratum containing as the essential heat-sensitive components (1) a 5-hydroxy-3-pyrrolin-2-one having a negative substituent in the 3-position and the general formula:

HO if R! wherein X is a negative substituent selected from the group consisting of quaternary onium and inium salts and carboxyl groups and groups hydrolyzable thereto, R is a member selected from the group consisting of hydrogen, monovalent hydrocarbon radicals of not more than 10 carbon atoms, amino and dialkylamino of 1-2 carbon atoms, the radicals R when separate are each selected from the group consisting of hydrogen, alkyl of 1-10 carbons, cycloalkyl of 4-6 carbons, aryl of 6-10 carbons and aralkyl of 7-10 carbons and when linked together constitute a single divalent hydrocarbon radical which forms with the 4- and 5-carbon atoms of the pyrrolinone ring a carbocyclic radical of 5-7 ring atoms, said substituted pyrrolinones being further characterized in that when substituted with the members recited, not more than one of the 4- and S-carbons have an aromatic substituent and (2) from 0.01 to 1.0 mole per mole of said 5-hydroXy-3-pyrrolin-2-one of a metal salt selected from the group consisting of cupric, ferrous, mercuric, and silver salts of monoand dibasic organic carboxylic acids of not more than 4 carbon atoms, said stratum having a coating weight of 20-500 milligrams per square decimeter.

2. An element according to claim 1 wherein said 10 stratum also contains a water-permeable organic colloid binding agent having protective colloid properties.

3. An element according to claim 1 wherein said metal salt is a cupric salt of an organic carboxylic acid of not more than 4- carbon atoms.

4. An element according to claim 1 wherein said metal salt is cupric acetate.

5. An element according to claim 1 wherein said support of low heat conductivity is a thin, flexible sheet.

6. An element according to claim 1 wherein said support is paper.

References Cited in the file of this patent UNITED STATES PATENTS 1,944,293 Martinez Jan. 23, 1934 1,976,302 Shepphard et a1. Oct. 9, 1934 2,910,377 Owen Oct. 27, 1959 2,950,987 Howard Aug. 30, 1960 2,995,468 Steiger Aug. 8, 1961 

1. A THERMO-SENSITIVE, IMAGE-RECORDING COPY ELEMENT COMPRISING A SUPPORT OF LOW THAT CONDUCTIVITY HAVING AN OUTER STRATUM CONTAINING AS THE ESSENTIAL HEAT-SENSITIVE COMPONENTS (1) A 5-HYDROXY-3-PYRROLIN-I-ONE HAVING A NEGATIVE SUBSTITUENT IN THE 3-POSITION AND THE GENERAL FORMULA: 